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271.
对分离自中国南方的H9N2亚型禽流感病毒A/Chicken/Guangxi/KMⅢ/99(H9N2)进行了MDCK细胞的连续传代和NA基因序列的初步分析.研究发现,病毒接种细胞36 h左右出现细胞病变(CPE),细胞肿胀变圆,聚集,脱落.流感病毒经MDCK细胞连续传代19代后,HA效价与亲代病毒相当.将传代获得的第19代病毒进行基因克隆,与亲代病毒进行序列比较,发现经传代后其HA1羧基端的分子特征是:R-S-S-R,仍属于非低致病力毒株. 相似文献
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Bill Domoney 《Research in Mathematics Education》2013,15(1):53-67
Previous research has shown that secondary school students’ understanding of fractions is dominated by the part-whole concept to the possible detriment of their understanding of a fraction as a number in its own right. The present paper reports on an investigation into the understanding of intending primary teachers in this area. Four representatives of a cohort of sixty students on a PGCE course specialising in the lower primary age range were asked detailed questions probing their knowledge of fractions. The conclusion was that the part-whole concept dominates. All of the students were familiar with the numerical concept from their work on the PGCE course, but they reverted to the more familiar part-whole ideas in attempting to solve problems. 相似文献
275.
In order to study the conceptions, and their evolutions, of the tangent line to a curve an updating workshop which took place in México was designed for upper secondary school teachers. This workshop was planned using the methodology of cooperative learning, scientific debate and auto reflection (ACODESA) and the conception-knowing-concept model (cK¢) developed mainly by Balacheff. In order to initiate the conceptions reorganization, an initial activity was made in the graphic frame; it seems optimal to start the debates without leading participants to failure. The mathematical core of the workshop was formed by an algebraic method to find tangents to algebraic curves which is close to Descartes’ method. The ACODESA methodology allowed some intense debates mainly concerning the local character of a tangent, generating the teachers’ cognitive unbalance which is a starting point for the refinement or transformation of their conceptions. On the other hand, the cK¢ model allows to understand the conceptions of participants and to analyze the evolution of their knowings. 相似文献
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利用束流能量为116MeV的59Co(35Cl,2p2n)90Mo反应布居90Mo的高自旋态.用10台反康普顿HPGe探测器组成的探测阵列进行γγ符合测量.通过多普勒展宽峰的形状分析测定90Mo高自旋态的寿命.在正宇称衰变系观察到增强的M1跃迁,推断I=13以上是扁椭形变.负宇称高自旋态具有大的B(E2)值,并随自旋增大而起伏变化.正、负宇称态之间的跃迁显示增大的E1跃迁,似有八极关联的可能.但是,90Mo并不处在理论预言的存在八极形变的核区内. 相似文献
279.
Efficient generalized conjugate gradient algorithms,part 1: Theory 总被引:14,自引:0,他引:14
The effect of inexact line search on conjugacy is studied in unconstrained optimization. A generalized conjugate gradient method based on this effect is proposed and shown to have global convergence for a twice continuously differentiable function with a bounded level set. 相似文献
280.
We prove two results about the problem of finding the Helly number for line transversals to a family of parallel triangles in the plane: (1) If each three triangles of a family of parallel right triangles are intersected by an ascending (or a descending) line, then there is an ascending (or a descending) line that intersects all 相似文献